A certified date from a notary public is used to objectively prove that a paper medium existed at a certain time point. This is because a claim of the existence of the paper medium made by the owner thereof himself/herself, even if he/she has made any, is not reliable and intervention by a trusted third party is therefore necessary.
In the meantime, various documents are recently more and more often created by information processing devices such as computers, and there has been an increasing demand for having the creation time and the content of created digital data certified by a third party. Under such existing circumstances, Patent Literature 1 discloses a technology for realizing an electronic notary service.
According to the description in paragraph [0028] of Patent Literature 1, a digital signature (131) of a consumer of a notary service and additional information (132) are added to electronic data (130) for which the notary service is desired, a digital signature (133) of an authorizer at a notary center is further added thereto to obtain the resulting data in an integrated state as certified electronic data (141). As a result of adding the digital signature (131), etc., in this manner, the electronic data (130) that used to be the original have become non-identical to the original electronic data. Since data for which certification is required are the original data before being modified, it is like putting the cart before the horse that the original data have to be modified for certification. Moreover, the additional information (132) contains the date, the authorizer, the authorized content, etc., and serves as a certificate of the electronic data (130), but a certificate should essentially be independent of the subject to be certified thereby and is not supposed to be added to data to be certified.